[node] Unobtrusive onchain operations

[LayneHaber]

All apps have to be collateralized, which means waiting for on-chain updates (i.e deposit/withdrawal) means bad UX.

Example: Streaming payments. End users could be waiting to receive more payments, but have them blocked by a pending deposit transaction.

Example: De-collateralizing. Intermediaries could be de-collateralizing a channel and users would not be able to make a payment until that transaction is mined.

[LayneHaber]

User story:

• User receives a payment that is not fully collateralized
• User also has $5 in their channel to spend
• Hub begins a deposit to collateralize users channel. This may be done in a way or for a reason that is nonobvious to the end user
• User cannot spend pre-existing $5 until the collateralizing deposit from the hub is cleared.

Ideally, this "pending deposit" would not affect the user's ability to spend their existing channel balance.

[ArjunBhuptani]

This is particularly an issue right now while gas prices are spiking and so transactions are sometimes taking 20 minutes to mine. Would suck to lose access to your channel for 20 minutes.

You could implement a timeout but then that introduces potential channel-breaking conditions where a deposit goes through AFTER timeout. Even if you enforce timeout onchain (somehow), this would mean poor UX because none of your deposits would work. (We're going through this exact problem in v1 right now)